1. Field of the Invention
The present invention relates to an apparatus for heating in a ladle molten metal, to be poured into a mold.
2. Discussion of the Related Art
In the case where the temperature of molten metal in a ladle to be poured into a mold falls so that the fluidity of the molten metal becomes less fluid than is required for proper molding procedures, the molten metal in the ladle may be returned to a melting furnace to be remelted. However, the remelting of cooled or solidified metal is undesirable because of considerable energy losses incurred.
Therefore, an induction heating apparatus has been developed for a ladle in which first cores are attached to a ladle adapted to be mounted on a supporting tray, to which second cores and a coil are fixed, to maintain the molten metal in the ladle in a fluid state at all times. Such an apparatus is conventional and disclosed in Japanese Patent Unexamined Publication No. Sho- 61-137521.
FIG. 17 of the accompanying drawings is a sectional view of the conventional apparatus. A ladle 1 includes metal shell body 2 made for a non-magnetic material such as stainless steel, and a refractory heat-insulating material 3 spread on the inside of the metal shell 2. Hanging rods 5, 5 are linked to trunnion shafts 4, 4 projecting from opposite sides of the metal shell 2. A driven wheel 6 for inclining the ladle is mounted to one trunnion shaft 4 First cores 8a and 8b, arranged in pairs circumferentially at intervals of a predetermined pitch are attached to the outer circumferential portion 3a and the outer bottom portion 3b of the refractory heat-insulating material 3. Second cores 11, corresponding in number and pitch to the first cores 8a and 8b, are fixed on a tray 10 which is fixed on a floor 9 for mounting the ladle 1 from above. A supporting member 12 for engaging the bottom portion of the ladle 1 and a stopper 13 for positioning the ladle 1 circumferentially are provided in the tray 10 so that the first cores 8a and 8b in each pair can be aligned with and face magnetic pole portions 11a and 11b provided at the opposite ends of corresponding one of the second cores 11 when the ladle 1 is put on the tray 10. Further, a coil 14 is wound on the second cores 11.
When the coil 14 is energized to excite the second cores 11, an alternating magnetic field 16 is produced in molten metal 15 in the ladle 1 through the first cores 8a and 8b to effect induction heating of the molten metal 15 to maintain the molten metal 15 in a suitably fluid state.
In the aforementioned conventional apparatus, the second cores 11 and the coil 14 for producing heating energy, together with power cables and water-cooled pipings (not shown), are fixed to the tray 10 side. Accordingly, the conventional apparatus has an advantage in that the structure for providing the tray related members can be simplified and the ladle 1 containing the molten metal 15 can be moved freely by hanging rods 5 or can be inclined by trunnion shafts 4.
However, the L-shaped configuration of the second cores 11 makes it difficult to produce the second cores 11. If the height of the magnetic pole portion 11b of each second core 11 and the height of the stopper 13 cannot be established accurately, the magnetic pole portion 11b may collide with some corresponding first core 8b in the bottom portion 3b of the ladle 1, causing breakage or the gap between the magnetic pole portion 11b and the first core 8b to be unacceptably large. This latter condition results in an increase of reluctance, increase of energy loss and abnormal heating of the ladle periphery.